The Yohkoh Software system allows customization of both site and user level IDL and operating system environments . These features are optional, and many users may work effectively without any knowledge or implementation of these features. On the other hand, as the Yohkoh system evolves at a given site, some of these features may be required to allow the Yohkoh system manager to tailor the system for the given site resources. For example, the multitude of Yohkoh ancillary databases may be divided among multiple disks or machines to match local disk resources. Sophisticated users may use some of these features to further customize the IDL environment while still remaining within the Yohkoh framework.